Document FR-2 715 499 discloses a puffer-type circuit-breaker comprising a casing filled with a dielectric gas under pressure, and two arcing contacts co-operating with each other, at least one of the arcing contacts being part of a moving contact assembly secured to a drive member and organized to be displaced axially inside the casing between a closed position and an open position on being driven during an opening operation, the moving contact assembly being made up of a first tube co-operating with a second tube that is coaxial with the first tube to define firstly a blast chamber on one e of a ring connected both to the first tube and to the second tube, and secondly a compression chamber on the other side of the ring, communicating with the blast chamber, and closed by a semi-moving piston, the circuit-breaker being provided with first means for holding the piston stationary during a first portion of the displacement stroke of the moving contact assembly between the closed position and the open position, and with second means for displacing the piston axially with the moving contact assembly during a second portion of the same displacement stroke of the moving contact assembly.
When low currents are to be interrupted, the arc that strikes between the arcing contacts during an opening operation is extinguished by means of the gas in the compression chamber being compressed. The flow of gas coming from the compression chamber extinguishes the arc before the end of the displacement stroke of the moving assembly. Therefore, it is not necessary to compress the gas in the compression chamber during the entire displacement stroke of the moving contact assembly. Once the piston starts moving with the moving assembly, the quantity of energy required to drive the moving contact assembly is very small because the gas is no longer compressed.
As disclosed in that prior document, the means comprise pneumatic means co-operating with mechanical means.
In a preferred embodiment described in that prior document, the second mechanical means for displacing the piston axially comprise an entrainment member associated with the moving contact assembly, which member entrains an abutment element, associated with the piston, during the second portion of the displacement stroke of the moving contact assembly, the abutment assembly being disposed in the path of the entrainment member. The first mechanical means for holding the piston stationary comprise a spring disposed between a stationary element and an end wall of the piston and a stationary retaining member that co-operates with an abutment wall of the piston. The pneumatic means are means for generating suction in the space lying between the stationary retaining member and the abutment wall, which space is made leak-proof.
Such an arrangement is relatively complex, and is costly to manufacture.